The general objective of this research is to elucidate the mechanisms by which the obligately intracellular parasitic bacteria of the genus Chlamydia penetrate, grow within membrane-limited vacuoles, and avoid natural defenses of host cells in culture. The following specific objectives will be pursued: a. Isolation of vacuoles containing C. psittaci 4 hours post-infection, characterization by PAGE of the membrane proteins surrounding the chlamydiae, and comparing these proteins to proteins in L-cell cytoplasmic membrane and in phagocytic membranes surrounding latex spheres. L-cell cytoplasmic membrane will be labelled with 125I using a lactoperoxidase coupled system. b. Using autoradiographic techniques, attempts will be made to determine mechanisms by which the inclusion membrane surrounding C. trachomatis (strain LGV) increases in surface area in the absence of host protein synthesis. c. C. psittaci absorbs to cells in culture efficiently whereas trachoma organisms do not. The role of hydrophobic forres in parasite-host cell interactions will be investigated using an aqueous polymer two-phase system.